As noted in U.S. application Ser. No. 08/970,832 filed in the names of Regelsberger et al, control of process conditions in an electrophotographic apparatus can be provided by forming toned density patches on the photoconductors. Such patches are formed by exposing, for example, interframe portions of the photoconductor to exposure light from the imaging source and developing same with the development station under appropriate electrical bias. By measuring the density of the patches, it can be determined whether adjustments are needed to one of the known operating process control parameters such as primary charger setpoint, exposure setpoint and development bias.
The density of the developed toned patches can be measured using a densitometer. One type, a transmission densitometer, projects light, visible or infrared, through an object onto a photodiode. The amount of energy reaching the photodiode determines the voltage output from the device.
In a copier/printer, the photoconductor passes between the light source and the photodiode. When the photodiode has toner on the surface, the amount of light reaching the photodiode is decreased. This changes the voltage output from the device, proportional to the optical density of the toner on the surface. Based on this voltage, the amount of toner applied to the photoconductor can be varied as required in order to obtain consistent image quality.
Another type of densitometer as described in U. S. Pat. No. 5,519,497 uses reflected flux rather than transmitted flux to determine density.
As these machines are used, contamination can build up on the surface of the photodiode, changing the voltage output. Typically, these devices are permanently fixed to the structure below the photoconductor, such that the photoconductor must be removed in order to clean the photodiode.
It is thus an object of this invention to provide a new and improved apparatus for locating the densitometer which eliminates the need to remove the photoconductor. This reduces the time required to perform maintenance on the machine, as well as reduces the risk of damage to the photoconductor. Other objects and advantages of the invention will become apparent from a reading of the specification taken in conjunction with the accompanying drawing.